The principal objective of this research is to investigate the regulation of the differentiation program in erythropoiesis. In order to do this, the mRNA of mouse carbonic anhydrase II has been cloned and characterized by a hybridization selection assay and DNA sequencing. The cloned cDNA has been used subsequently to show that induction of mouse erythroleukemic cells to differentiate to erythrocytes results in increased transcription of the carbonic anhydrase II gene, corresponding to the increase of its protein. Several different carbonic anhydrase chromosomal genes have been cloned, using the cloned cDNA as a probe. After characterization of these clones, they will be compared with those of alpha-beta-major-\and beta-minor-globin to identify the basis of their coordinated expression. Work continues to clone additional mRNAs of erythroid cells to extend this study.